An antenna (e.g., a dipole antenna) typically generates radiation in a pattern that has a preferred direction, i.e., the generated pattern is stronger in some directions and weaker in other directions. When receiving electromagnetic signals, the antenna has the same preferred direction, i.e., received signal is strongest in the preferred direction. Therefore, signal quality (e.g., signal to noise ratio) can be improved by aligning the preferred direction of the antenna with a target receiver or a source of signal. However, it is often impractical to physically reorient the antenna and/or the exact location of the target may not be known. To overcome some of the above shortcomings of the antenna, a phase array antenna can be formed from a set of antennas to simulate a large directional antenna. An advantage of the phase array antenna is its ability to transmit/receive signals in a preferred direction (i.e., its beamforming ability) without physically repositioning or reorienting the antenna.
FIG. 1 is a schematic illustration of a phase array antenna system 10 according to prior art. The illustrated system has a phase array antenna 14 that includes four individual antennas 14i that are set apart by a half wavelength (λ/2) of the transmitted signal. A transmitter 12 generates signals for the phase array antenna 10. The transmitter 12 includes a modulator that receives two inputs (a baseband signal and a carrier oscillator) and outputs a modulated radio frequency (RF) signal. For example, a baseband signal having a relatively low frequency can be modulated by a carrier oscillator having a relatively high frequency to produce the modulated RF signal. The resulting modulated RF signal is transmitted through a beamformer 20 that adjusts amplitude and phase of the RF signal by applying an amplitude adjustment (ai) and a phase shift (θi) to the RF signal. A combination of the amplitude and phase adjustment for each individual antenna 14i is called a complex weight (wi) for that antenna. Since the resulting adjusted RF signal (i.e., adjusted by applying the complex weight) is generally a low power signal, power amplifiers 38i amplify RF signal that leaves the beamformer 34. Amplified RF signals arrive at the individual antennas 14i, and are transmitted to surrounding space as a wireless signal. In the illustrated example in FIG. 1, the wireless signal is transmitted in a direction D, i.e., a front F of the wireless signal makes an angle α (angle of antenna or AoA) with respect to the plane of the antennas 14i. The desired direction D of the wireless signal can be achieved by, for example, programming the beamformer 20 such that θ1>θ2>θ3>θ4 by appropriate Δθ, such that the front F makes angle α (AoA) with the plane of the antennas 14i. Analogously, if the phase array antenna 14 is a receiver and a source of RF signal (i.e., a transmitter) is located in at AoA D′, the distribution of θi's can be adjusted such that the phase array antenna has a maximum sensitivity in the direction D′.
However, in addition to the desired, controlled changes to phase θi of the individual antennas 14i, the system may introduce undesired changes to phase θi. For example, high frequency RF signals (e.g., GHz range) are characterized by short wavelengths (e.g., mm range wavelegths). Consequently, even a relatively small difference between the length Ti of transmission lines 19i (e.g., mm or sub-mm differences) may result in appreciable deviation from the desired distribution of θi's, which, in turn, causes errors in the AoA, loss of sensitivity, spurious/undesired lobes around the AoA, and other issues. One approach to minimize these issues is described in relation to FIG. 2 below.
FIG. 2 is a schematic view of a phase array antenna system 200 in accordance with prior art. The illustrated phase array antenna 14 includes seven individual antennas 14i spaced apart by half wavelength (λ/2) of the transmitted signal. The transmitter 12 generates RF signals that are routed to the antennas 14i through traces 29i. The signals in the individual traces 29i can be phase shifted to produce desired AoA of the outgoing wireless signal. As explained above, differences in the length Ti among individual traces 29i can introduce undesirable variations in the phase shifts (θi's) of the individual antennas 14i, especially for the signals in the GHz frequency range. Therefore, with the illustrated conventional system, all traces 29i have uniform length to eliminate/minimize the unwanted variability in the phase of signal transmitted through the traces. However, such uniform length must necessarily correspond to at least the distance from the transmitter 12 to the peripheral antennas 14i. As a result, the traces 29i that connect the transmitter 12 with the centrally located antennas 14i are longer than necessary, which causes additional signal power loss in these traces. Accordingly, it would be advantageous to provide traces that connect the transmitter/receiver with the antennas such that the changes of phase θi caused by the traces are minimized, while not introducing an undesirable power loss.